The present invention relates generally to completion operations performed in subterranean wells and, in an embodiment described herein, more particularly provides a tool for use in these operations and methods of using same.
Completion operations in which a slurry is pumped down a tubing string to a formation intersected by a subterranean well are well known in the art. For example, formation fracturing and gravel packing operations each in part utilize slurry delivery to accomplish their objectives. In each of these operations, downhole fluid pressure at the point at which the slurry interfaces with the formation should be maintained within an appropriate range and varied as conditions dictate, and a fluid portion of the slurry may be returned to the earth's surface.
In some service tools used in fracturing operations, the tools may be configured to prevent return of the fluid portion during slurry delivery, so that the entire slurry is injected into the formation. In some of these tools, the tool may be manipulated by displacing the tubing string at the earth's surface to selectively permit return of the fluid portion to the earth's surface. Of course, since fluid return is typically via an annulus formed between the tubing string and casing lining the wellbore, return flow of the fluid portion therethrough may also be controlled at the earth's surface by utilizing a valve connected to the annulus at the earth's surface, however, this method requires applying relatively high pressure to the annulus and, therefore, is usually undesirable.
It would be useful to be able to selectively permit return of the fluid portion downhole, without requiring manipulation of the tubing string, and without requiring application of fluid pressure to the annulus. It would further be useful for the selection to be performed automatically, for example, in a combined fracturing and gravel packing operation, return of the fluid portion could be permitted automatically upon conclusion of the fracturing operation.
In some circumstances, it may be desirable to be able to regulate a rate of return of the fluid portion. Varying the rate of return of the fluid portion would permit corresponding regulation of the fluid pressure of the slurry downhole. It would also permit varying the rate of slurry particulate matter injected into the formation and/or deposited in the annulus.
Furthermore, particularly in fracturing operations, it is quite common for fluid pressure increases to be experienced near the end of the operation. These fluid pressure increases may be damaging to the downhole equipment and/or the well. What is needed in this circumstance is a way to immediately relieve the fluid pressure downhole, so that a fluid pressure increase does not exceed a predetermined maximum level.
In order to accurately monitor fluid properties near the formation during fracturing and/or gravel packing operations, a tool is needed that is able to communicate with the operator at the earth's surface. In this way, the operator would be able to adjust the operation in conformance with downhole conditions. The tool should include one or more sensors to sense the fluid properties, and a way to transmit data to the earth's surface.
From the foregoing, it can be seen that it would be quite desirable to provide a tool for use in welisite operations which permits downhole regulation of fluid pressure, which permits selective return circulation, which is able to limit fluid pressure downhole, and which can communicate with the earth's surface. It is accordingly an object of the present invention to provide such a tool and associated methods of using the tool.